Brake actuator apparatus and method for actuating a brake

ABSTRACT

A brake actuating apparatus includes a force transmission element operable to transmit a brake actuating force and an abutment member moveable to abut the force transmission element. A piezo-electric device operable on expansion applies a force between the abutment member and the force transmission element to move the force transmission element in a direction of brake actuation. A support member moveable independently of the abutment member supports the force transmission element in the new position following expansion of the piezo-electric device.

This application claims priority to PCT application PCT/GB02/01463 filedon Mar. 27, 2002, which claims priority to Great Britain patentapplication GB0110438.9 filed Apr. 27, 2001.

TECHNICAL FIELD

The present invention relates to a brake actuator apparatus and methodfor actuating a brake.

BACKGROUND OF THE INVENTION

A known vehicle braking system includes a disc fixed for rotation with awheel and a brake clamping mechanism including a tappet mechanicallyactuated to bring brake pads into contact with the disc and to apply aforce between the pads and the disc to provide frictional braking.

Piezo-electric devices, which expand when energized by an electricvoltage, are known for applying a mechanical actuating force over ashort distance.

SUMMARY OF THE INVENTION

The brake actuating apparatus of the present invention includes a forcetransmission element operable to transmit a brake actuating force and anabutment member moveable to abut the force transmission element. Apiezo-electric device operable on expansion applies a force between theabutment member and the force transmission element to move the forcetransmission element in a direction of brake actuation. A support memberis moveable independently of the abutment member to support the forcetransmission element in its new position following expansion of thepiezo-electric device.

Preferably, the piezo-electric device is fixed for movement with thefirst abutment member. Alternately, the piezo-electric device may befixed for movement with the force transmission element.

Preferably, the apparatus further includes a body member. The abutmentmember has a threaded portion in threaded engagement with the bodymember to be moveable by relative rotation between the abutment memberand the body member.

Preferably, the support member includes a threaded portion in threadedengagement with a second body member of the apparatus and is axiallymoveable by relative rotation between the support member and the secondbody member.

The abutment member and support member are rotatable by respectiverotation devices. Alternately, the body member and the second bodymember are rotatable by respective rotation devices. Preferably, therotation devices are electric motors.

For releasing the brake, the support device is arranged to support theforce transmission element for movement of the abutment member, with thepiezo-electric device contracted, to a position wherein expansion of thepiezo-electric device causes the abutment member to abut the forcetransmission element. The support member is moveable to a positionwherein contraction of the piezo-electric device allows the forcetransmission element to move into abutment with the support member.

A method for actuating a brake includes moving an abutment member intoabutment with a force transmission element operable for transmitting abrake actuating force. A piezo-electric device expands to apply a forcebetween the abutment member and the force transmission member to movethe force transmission element in a direction of brake actuation. Asupport member is moved into abutment with the force transmissionelement to support the force transmission element in its new position,and the piezo-electric device is contracted. These steps are repeated asmany times as required to actuate the brake. When the brake is to bereleased, the force transmission element is supported by the supportmember and the piezo-electric device contracts, moving the abutmentmember out of abutment with the force transmission element. Thepiezo-electric device is expanded, and causing the abutment member toabut the force transmission element. The support member is moved awayfrom the force transmission element, contracting the piezo-electricdevice, causing the support member to support the force transmissionelement. These steps are repeated as many times as required to releasethe brake.

Although the distance the piezo-electric device moves is small, byrepeatedly expanding and contracting the device and moving the abutmentmember and support member to abut the force transmission element, thepiezo-electric device may be used to provide a substantially largermovement to the force transmission element.

A braking mechanism has a degree of elasticity in its structure, and adegree of elastic deformation has to be taken up by the structure beforethe force applied by the actuating device is transmitted to the brakepads. The piezo-electric device may be used to move the forcetransmission element beyond the elastic deformation of the structure andto apply the braking force.

A further advantage is that the same apparatus may also be used torelease the brake.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by way of example,with reference to the accompanying drawings in which:

FIGS. 1 a to 1 e show the stages in the operation of a brake actuatorthat applies an actuating force; and

FIGS. 2 a to 2 d show the stages in the operation of the actuator ofFIGS. 1 a to 1 e for releasing the brake.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 a shows an actuator 5 for actuating a brake 24 including anabutment member in the form of a pin 10 arranged on an axis of theactuator 5. The pin 10 has a threaded portion 11 in threaded engagementwith an associated first body member 12 of a vehicle brake mechanism.The first body member 12 is axially fixed with respect to the brakemechanism. A piezo-electric device 14 including at least onepiezo-electric element is fixed to the pin 10 and is expandable byapplication of an electric voltage. The pin 10 abuts a forcetransmission element in the form of a tappet 16 for transmitting anapplied actuating force in an axial direction. The tappet 16 forms partof a clamping mechanism for exerting a clamping force on a pair of brakepads in response to application of the brake 24.

A support member in the form of a sleeve 18 has a threaded portion 19 inthreaded engagement with an associated second body member 20 of thebrake mechanism. The second body member 20 is axially fixed with respectto the brake mechanism. The sleeve 18 is substantially coaxial with andsurrounds the pin 10. The sleeve 18 abuts the tappet 16 to support it.

The engagement of the threaded portions 11 and 19 of the pin 10 and thesleeve 18, respectively, provide axial movement by relative rotationbetween the pin 10 and the sleeve 18 and their respective associatedbody members 12 and 20. Rotational motion is provided to the pin 10 orthe sleeve 18 by associated electric motors 22. Alternately, rotationalmotion may be provided to the first and second body members 12 and 20,respectively.

The piezo-electric device 14 does not have to directly abut the tappet16 (as shown in FIGS. 1 a to 1 e and 2 a to 2 e), but may be situated atany position along the length of the pin 10 so that expansion of thepiezo-electric device 14 causes the pin 10 to abut the tappet 16 and toapply a force in the axial direction. Alternately, the piezo-electricdevice 14 can be attached to the tappet 16.

Referring to FIG. 1 b, in the first stage of actuation of the brake 24,the piezo-electric device 14 is expanded by application of the electricvoltage to apply a force to the tappet 16 and move the tappet 16 in theaxial direction out of contact with the sleeve 18.

In the second stage, as shown in FIG. 1 c, the sleeve 18 is rotated tomove axially to abut the tappet 16.

In the third stage, as shown in FIG. 1 d, the piezo-electric device 14is contracted by removal of the electric voltage, moving the pin 10 outof contact with the tappet 16.

In the fourth stage, as shown in FIG. 1 e, the pin 10 is rotated to moveaxially to abut the tappet 16. The actuator 5 is in the sameconfiguration as in FIG. 1 a, although the tappet 16, the pin 10, andthe sleeve 18 have been moved in the axial direction.

The stages shown in FIGS. 1 a to 1 e are repeated as many times asrequired to take up the elastic deformation of the brake mechanism andto apply the required braking force to the brake 24.

Although only a small movement of the tappet 16 can be affected by asingle expansion of the piezo-electric device 14, the brake 24 can beactuated by repeated expansion and contraction of the piezo-electricdevice 14.

Referring to FIG. 2 a, in the first stage of releasing the brake 24, thepin 10 is rotated to move a first predetermined distance axially awayfrom the tappet 16.

The first predetermined distance is set such that in the second stage,as shown in FIG. 2 b, the piezo-electric device 14 is expanded to abutthe tappet 16 and move the tappet 16 just clear of the sleeve 18.

In the third stage, shown in FIG. 2 c, the sleeve 18 is rotated to movea second predetermined distance axially away from the tappet 16.

The second predetermined distance is set such that in the fourth stage,as shown in FIG. 2 d, the sleeve 18 is in a position such that, when thepiezo-electric device 14 is contracted, the tappet 16 moves axially tojust abut the sleeve 18 before the piezo-electric device 14 has fullycontracted.

The stages shown in FIGS. 2 a and 2 d are repeated to further releasethe brake 24.

The foregoing description is only exemplary of the principles of theinvention. Many modifications and variations of the present inventionare possible in light of the above teachings. The preferred embodimentsof this invention have been disclosed, however, so that one of ordinaryskill in the art would recognize that certain modifications would comewithin the scope of this invention. It is, therefore, to be understoodthat within the scope of the appended claims, the invention may bepracticed otherwise than as specifically described. For that reason thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. A brake actuating apparatus comprising: a force transmission elementpositioned at a first position that transmits a brake actuating force;an abutment member that is moveable to cause a piezo-electric device toselectively abut and disengage from the force transmission element; thepiezo-electric device being expandable to apply a force between theabutment member and the force transmission element to move the forcetransmission element in a direction of brake actuation; and a supportmember moveable independently of the abutment member to support theforce transmission element stationary in a new position followingmovement of the force transmission element from the first position byexpansion of the piezo-electric device and to allow the abutment memberto move the piezo-electric device so that the piezo-electric device isexpandable to apply the force between the abutment member and the forcetransmission element to move the force transmission element from the newposition in the direction of brake actuation, wherein the support memberand the abutment member are co-axially arranged, wherein the abutmentmember includes a first threaded portion in threaded engagement with afirst body member and the abutment member is moveable by relativerotation between the abutment member and the first body member, andwherein the support member includes a second threaded portion inthreaded engagement with a second body member and the support member isaxially moveable by relative rotation between the support member and thesecond body member.
 2. The brake actuating apparatus according to claim1 wherein the piezo-electric device is attached to the abutment member.3. The brake actuating apparatus according to claim 1 wherein at leastone of the abutment member and the support member is rotatable by arotation device.
 4. The brake actuating apparatus according to claim 3wherein the rotation device is an electric motor.
 5. The brake actuatingapparatus according to claim 1 wherein at least one of the first bodymember and the second body member is rotatable by a rotation device. 6.The brake actuating apparatus according to claim 3 wherein the rotationdevice is an electric motor.
 7. The brake actuating apparatus accordingto claim 1 wherein, with the piezo-electric device in a contractedposition, the support member supports the force transmission element formovement of the abutment member to an abutment member position whereinexpansion of the piezo-electric device causes the piezo-electric deviceto abut the force transmission element, and the support member ismoveable to a support member position wherein contraction of thepiezo-electric device allows the force transmission element to abut thesupport member.
 8. A method for actuating a brake comprising the stepsof: moving an abutment member to abut a piezo-electric device against aforce transmission element operable for transmitting a brake actuatingforce, wherein the abutment member is moveable to cause thepiezo-electric device to selectively abut against and disengage from theforce transmission element, wherein the abutment member includes a firstthreaded portion in engagement with a first body member, and theabutment member moves by relative rotation between the abutment memberand the first body member; expanding the piezo-electric device to applya force between the abutment member and the force transmission elementto move the force transmission element in a direction of brake actuationfrom a first position into a second position; moving a support memberindependently of the abutment member into abutment with the forcetransmission element to support the force transmission element in thesecond position, wherein the support member includes a second threadedportion in engagement with a second body member, and the support membermoves by relative rotation between the support member and the secondbody member and wherein the support member and the abutment member areco-axially arranged; contracting the piezo-electric device; repeatingthe step of moving the abutment member; and expanding the piezo-electricdevice to apply the force between the abutment member and the forcetransmission element to move the force transmission element in thedirection of brake actuation from the second position to a thirdposition.
 9. The method for actuating a brake according to claim 9further comprising the steps of: moving the abutment member out ofabutment with the force transmission element while the forcetransmission element is supported by the support member and thepiezo-electric device is contracted; expanding the piezo-electric deviceto abut the abutment member on the force transmission element; movingthe support member away from the force transmission element; contractingthe piezo-electric device to cause the support member to support theforce transmission element; and repeating the steps of moving theabutment member, expanding the piezo-electric device, moving the supportmember, and contracting the piezo-element to release the brake.